This invention relates to variable capacity wobble plate compressors mainly adapted for use in air conditioning systems for automotive vehicles, and more particularly to an improved wobble plate compressor in which the crankcase pressure is controllable for varying the displacement or capacity of the compressor.
A variable capacity wobble plate compressor in general is adapted to vary its displacement or capacity through a change in the angularity of the wobble plate. It is known e.g. from U.S. Pat. No. 3,861,829 to vary the refrigerant pressure in the crankcase for changing the angularity or angle of inclination of the wobble plate relative to the drive shaft. A conventional wobble plate compressor of this type comprises a fluidtight housing, a drive shaft rotatably disposed in the housing, a cylinder block arranged in the housing and formed therein with a plurality of cylinders circumferentially arranged around the drive shaft and extending substantially parallel to the axis of the drive shaft, pistons received in the respective cylinders for reciprocating motions therein, and a wobble plate supported at its diametrically central portion by trunnion pins extending at right angles to the drive shaft and axially movable therealong and also supported at its peripheral edge by a pivot pin rotatable about the drive shaft together therewith. The wobble plate is adapted to be pivotally displaced in unison with axial movement of the trunnion pin along the drive shaft to have its angularity varied relative to the drive shaft. As the wobble plate rotates in a position inclined relative to the drive shaft, the pistons are reciprocatingly moved in their respective cylinders for pumping actions. In the compressor, the resultant reaction force exerted by all the pistons, (some on their compression strokes and some on their suction strokes) acts upon the wobble plate at a point inside a half portion of the circumference described by the axes of the cylinders, which is located at the same side of the drive shaft as the pistons on their compression strokes, so that the wobble plate is acted upon by the above resultant reaction force to become inclined relative to the drive shaft about the trunnion pins as a movable fulcrum during the pumping actions of the pistons. The resultant reaction force of the pistons counteracts the pressure in the crankcase which acts upon the pistons as back pressure. Therefore, when there occurs a drop in the pressure in the crankcase, the wobble plate is displaced in the angularity-increasing direction to increase the capacity, whilst when there occurs an increase in the crankcase pressure, the wobble plate is displaced in the angularity-decreasing direction to decrease the capacity.
In the above patented wobble plate compressor, a diaphragm valve is arranged across a line connecting the crankcase with a zone under lower pressure in the refrigerating circuit of an air conditioner, and operable in response to the refrigerant pressure in the line so that when a drop occurs in the line pressure due to a decrease in the thermal load on the refrigerating circuit, the diaphragm valve is displaced to restrict the communication between the interior of the crankcase and the lower pressure zone in the refrigerating circuit to reduce the flow rate of blow-by gas (which leaks into the crankcase through the gaps between the cylinders and the pistons) to the lower pressure zone through the line, resulting in an increase in the crankcase pressure. Consequently, the angularity of the wobble plate decreases to reduce the displacement of the compressor. On the contrary, when the refrigerant pressure in the line rises due to an increase in the thermal load on the refrigerating circuit, the crankcase pressure decreases to cause an increase in the angularity of the wobble plate to obtain increased displacement of the compressor.
Therefore, according to the above compressor patent, in the event that it is desired to suddenly reduce the displacement of the compressor (for instance, when it is desired to temporarily relieve an automotive engine associated with the compressor of the compressor load to use the total engine output for driving the automotive vehicle on which the engine is installed, in accelerating the vehicle or during running of same on an ascending slope) a stop valve (zero-stroke valve) which is arranged across the aforementioned line is closed to interrupt the communication between the crankcase and the lower pressure zone in the refrigerating circuit. However, an increase in the crankcase pressure depends solely on the leakage of blow-by gas through the gaps between the cylinders and the pistons into the crankcase, which takes place after the above interruption. This is disadvantageous in obtaining a sudden reduction of the capacity of the compressor.